It is in Swamp, about 59 steps south-east of the spot the map marks with that name.

And 4 down from the surface once you are there.

• 1 — Swamp, as the map itself names it
• 2 — the ground above the treasure

• A rope. You drop in through a hole, and a rope is how you climb back out.
• Something for beholder, slime and mummy — they live down there.

The chest is 4 floors under the surface. Going down over it, this is what each floor uses:

1. Ground: down through a hole.
2. 1 down: down through a ladder.
3. 2 down: down through a ladder.
4. 3 down: down through a hole.

• 1 — the way in: a hole, ground
• → — the treasure lies this way

• 2 — a ladder, 1 down
• → — the treasure lies this way

• 3 — a ladder, 2 down
• → — the treasure lies this way

• 4 — a hole, 3 down
• → — the treasure lies this way

• 1 — the chest

One chest, one reward.